Cardiac pacing involves the electrical stimulation of the heart in order to control the timing of the contractions of the heart. Electrical stimuli in the form of pulses are generated by an implantable, battery-powered pacemaker, and are applied to the tissue of the heart by one or more electrodes that are connected to the pacemaker via flexible, insulated conductors. The insulated conductors and associated electrodes form what is referred to as the "lead."
Implantation is typically performed by inserting the distal end of the lead into the patient's cephalic vein (one of the main veins from the upper arm), and forwarding the distal end through the subclavian vein and superior vena cava into the right side of the heart. To maintain the stiffness of the lead during implantation, a guidewire or "stylet" is typically inserted into a lumen (hollow channel) of the lead. Once the lead is properly positioned within the heart (using fluoroscopy to view the distal end of the lead), the stylet is withdrawn, and the proximal end of the lead is connected to the pacemaker. Finally, the pacemaker is implanted beneath the skin.
For various disorders it is desirable to pace the heart by applying separate electrical stimuli to the atrium and the ventricle of the right side of the heart. This form of pacing, commonly known as dual-chamber pacing, generally requires the placement of an atrial electrode in the right atrium and a ventricular electrode in the right ventricle. In addition to applying electrical stimuli to the tissue of the respective chambers, one or both of these electrodes may be used to sense intrinsic electrical activity, and to thereby detect timing abnormalities. For example, the pacemaker may sense the naturally-occurring electrical activity in the right atrium and use this information to generate appropriate electrical stimuli to apply to the right ventricle.
One problem with dual-chamber pacing has been the need to separately position and maintain the atrial and ventricular electrodes in contact with the electrically-sensitive tissue of the respective chambers. Under current practice, two separate leads are implanted within the patient's heart--an atrial lead which provides connectivity between the pacemaker and the tissue of the right atrium, and a ventricular lead which provides connectivity between the pacemaker and the tissue of the right ventricle. In addition, various styles of leads have been proposed which include both the atrial and ventricular electrodes on a single lead body. (See, for example, U.S. Pat. Nos. 4,154,247; 4,567,901; 4,643,201; 4,393,883; 4,497,326; and 4,711,027.) These leads are generally referred to as single-pass atrio-ventricular (A-V) leads. Although many different styles of single-pass A-V leads have been proposed, none of these leads have gained acceptance in the medical community.
Although the use of separate atrial and ventricular leads desirably permits the physician to independently manipulate and position the atrial and ventricular electrodes during implantation, the use of two leads also creates a number of potential problems. For example, the leads may become damaged as the result of abrasion as the leads rub against each other within a blood vessel and/or within the heart. Additionally, the use of two separate leads often increases the likelihood of "subclavian crush," which is the crushing of the lead hardware (typically during patient motion) between the first rib and the clavicle. Further, the use of two leads typically requires the physician to make a larger incision in the cephalic vein (or other blood vessel) than is necessary for the implantation of a single lead. These problems with the current practice can potentially be solved by the use of a suitable single-pass A-V lead.
In order to gain acceptance in the medical community, it is important that a single-pass A-V lead be easy to implant. Moreover, it would be desirable to provide a single-pass A-V lead for which the implantation procedure is highly similar to the procedure currently used by physicians for the implantation of separate atrial and ventricular leads; this would allow physicians to begin implanting the new lead with minimal training. The present invention seeks to provide a single-pass A-V lead having these and other advantageous characteristics.